Steering system

ABSTRACT

A rack shaft has a rolling contact surface on the opposite side of rack teeth across an axis line X, and a pair of slanted surfaces extending in parallel with the axis line across the rolling contact surface. Furthermore, a roller rolling on the rolling contact surface of the rack shaft and an urging member having contact with the pair of slanted surfaces for applying an urging force are provided. The urging member is attached to the housing, forms an annular configuration surrounding the entire circumference of the rack shaft, and has contact portions having contact with the pair of slanted surfaces to apply the urging force.

TECHNICAL FIELD

The present invention relates to a steering apparatus, and moreparticularly, to a rack-and-pinion steering apparatus which includes arack shaft and a pinion.

BACKGROUND ART

One known type of steering apparatus of a vehicle is a rack-and-pinionsteering apparatus in which a rotational force and an amount of rotationof a pinion are converted into a thrust in the axial direction and astroke of a rack shaft by meshing engagement of the rack teeth of therack shaft with the pinion. Here, in some of rack holding mechanisms forholding a rack, the transmission efficiency has been improved, and thesteering torque has been reduced by providing a rolling rack guide,etc., which can support the rack by a roller, etc., rotating at aholding part for holding the back surface (the opposite side of the rackteeth) of the rack shaft.

At the same time, a so-called Y-type rack shaft, which is produced byforging to have a Y-type (shaped) section orthogonal to the axis line,has been developed in order to improve the strength of the rack teeth.An example, in which such a Y-type rack shaft and the rolling rack guidedescribed above are applied to a steering apparatus, is shown in FIG. 4.In FIG. 4, an output shaft 3 extending horizontally in a housing 1 isconnected to an unillustrated steering shaft, and rotatably supported bybearings 5, 6 with respect to the housing 1. The inner ring of thebearing 6 is fixed to the end of the output shaft 3 by a nut 8, and theouter ring of the bearing 6 is attached to the housing 1 by screwing afixing member 9, which also serves as a cover member.

The housing 1 is provided with a hollow columnar portion 1 c formed fromthe circumference of the rack shaft 10, which is a Y-type rack shaft,extending upward in the figure. A supporting unit 20 is disposed in thehollow columnar portion 1 c. The supporting unit 20 includes asubstantially cylindrical holder 21, a pin 22 contained in a groove 21 aof the holder 21, a roller 24 rotatably supported by a bearing 23 withrespect to the pin 22, a pipe-shaped screw member 25 for attaching theholder 21 to the hollow columnar portion 1 c, a disc spring 24A disposedbetween the holder 21 and the screw member 25 for urging the holder 21to the rack shaft 10 against the screw member 25, and a lock member 26of the screw member 25.

The rack shaft 10 has a pair of slanted surfaces 10 c, 10 c on bothsides across a cylindrical surface 10 b provided on the opposite side ofrack teeth 10 a in mesh with a pinion 3 a of the output shaft 3. Theroller 24 has an integral structure connecting a pair of truncated cones24 a, 24 a by a cylindrical portion 24 b. The truncated cones 24 a, 24 aare disposed rotatably along the slanted surfaces 10 c, 10 c of the rackshaft 10, respectively, thereby having a function of restraining arotational displacement of the rack shaft 10.

Here, when a strong force is transmitted between the output shaft 3 andthe rack shaft 10, such a force is supported by the supporting unit 20.Since the roller 24 has a structure described above, the slantedsurfaces 10 c, 10 c of the rack shaft 10 enters into the truncated cones24 a, 24 a and acts so as to push and spread them by a so-called wedgeaction. Thus, the truncated cones 24 a, 24 a deform as shown by thedotted line in the figure, thereby disadvantageously hindering thesmooth rotation. To cope with this, an increase in the rigidity of theroller 24 can be considered in order to restrain the deformation of thetruncated cones 24 a, 24 a. However, in order to restrain thedeformation against the wedge action, it is necessary to construct theroller 24 to be considerably strong. Thus, there is a problem in thatthe entire steering apparatus becomes large and heavy.

The present invention has been made in view of the problems of theseconventional techniques, and it is an object of the present invention toprovide a steering apparatus having a light-weight and compactconfiguration and capable of supporting the Y-type rack shaft moreappropriately.

In order to achieve the above object, according to the presentinvention, there is provided a steering apparatus including:

a housing; a rack shaft connected to a steering mechanism, having rackteeth formed at least on part of an outer surface, and movably supportedwith respect to the housing; and a pinion connected to a steering wheeland having meshing engagement with the rack teeth,

wherein the rack shaft is provided with a rolling contact surface on theopposite side of the rack teeth across an axis line and a pair ofsurfaces extending in parallel with an axis line on both sides acrossthe rolling contact surface,

the apparatus further comprises a rolling member rolling on the rollingcontact surface of the rack shaft and an urging member having contactwith the pair of surfaces and applying an urging force,

wherein the urging member is attached to the housing, forms an annularconfiguration surrounding the entire circumference of the rack shaft,and has a contact portion having contact with the pair of surfaces toapply an urging force.

By the steering apparatus according to the present invention, in thesteering apparatus including: a housing; a rack shaft connected to asteering mechanism, having rack teeth formed at least on part of anouter surface, and movably supported with respect to the housing; and apinion connected to a steering wheel and having meshing engagement withthe rack teeth, the rack shaft is provided with a rolling contactsurface on the opposite side of the rack teeth across an axis line and apair of surfaces extending in parallel with an axis line on both sidesacross the rolling contact surface. Furthermore, the apparatus includesa rolling member rolling on the rolling contact surface of the rackshaft and an urging member having contact with the pair of surfaces andapplying an urging force, wherein the urging member is attached to thehousing, forms an annular configuration surrounding the entirecircumference of the rack shaft, and has a contact portion havingcontact with the pair of surfaces to apply an urging force. Therefore,the force exerted on the rack shaft by the pinion can be supported bythe rolling member contacting with the rolling contact surface.Moreover, it is possible to restrain a rotational displacement of therack shaft about the axis line by applying the urging force against thepair of surfaces of the rack shaft by the contacting portion of theurging member. Also, since the urging member has an annularconfiguration, it is advantageously possible to easily attach/detach theurging member to/from the housing without using a connecting member suchas adhesive or a screw.

Furthermore, the contact portion of the urging member preferablyincludes a pressing portion having the shape of a cantilever.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating part of a rack-and-pinionsteering apparatus according to the present embodiment.

FIG. 2A is a sectional view illustrating part of the rack-and-pinionsteering apparatus according to the present embodiment, cut off at adifferent position from the position in FIG. 1. FIG. 2B is a viewillustrating the configuration in FIG. 1 as viewed in the arrowdirection IIB. FIG. 2C is a view illustrating the configuration in FIG.2B, cut off by the line IIC-IIC as viewed in the arrow direction.

FIG. 3 is an extracted perspective view of a rack shaft, a cylindricalroller, and an urging member of the present embodiment.

FIG. 4 is a sectional view illustrating part of a rack-and-pinionsteering apparatus to be compared with the present embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, a description will be given of an embodiment of thepresent invention based on the drawings.

FIG. 1 is a sectional view illustrating part of a rack-and-pinionsteering apparatus according to the present embodiment. In FIG. 1, anoutput shaft 103 horizontally extending in the housing 101 is connectedto an unillustrated steering shaft, and is rotatably supported by sealedbearings 105, 106 with respect to the housing 101. The inner ring of thebearing 106 is fixed to the output shaft 103 by a nut 108 screwed on theoutput shaft 103. The outer ring of the bearing 106 is attached to thehousing 101 by screwing a fixing member 109, which also serves as acover member. A pinion 103 a of the output shaft 103 has meshingengagement with rack teeth 110 a of a rack shaft 110 whose both ends areconnected to tie rods of an unillustrated traveling wheel steeringmechanism.

The housing 101 is provided with a hollow columnar portion 101 c formedfrom the circumference of the rack shaft 110 extending upward in thefigure. A supporting unit 120 is disposed in the hollow columnar portion101 c. The supporting unit 120 includes a cylindrical holder 121, a pin122 whose both ends are attached to a groove 121 a of the holder 121, acylindrical roller 123, which is a rotating member disposed about thepin 122, a needle bearing 127 rotatably supporting the cylindricalroller 123 with respect to the pin 122, a screw member 125 for attachingthe holder 121 to the hollow columnar portion 101 c, a disc spring 124disposed between the screw member 125 and the holder 121 for urging theholder 121 to the rack shaft 110, and a lock member 126 of the screwmember 125. By adjusting the amount of screwing of the screw member 125,the amount of compression of the disc spring 124 is changed, therebymaking it possible to adjust the pressing force to the rack shaft 110.After the adjustment, the screw member 125 can be locked by the lockmember 126 to prevent the screw member 125 from being loosened.

On the rack shaft 110, on the opposite side (called back surface side)of the rack teeth 110 a across the axis line X, in a cross sectionorthogonal to an axis line X shown in FIG. 1, a rolling contact surface110 b is formed at the upper center, and slanted surfaces (a pair ofsurfaces) 110 c, 110 c slanting in the facing direction each other areformed on both sides at the place lowered one step. Such a rack shaft iscalled a Y-type rack shaft, and is formed by forging work in the presentembodiment. The rolling contact surface 110 b is formed as a convexcurved surface, and the circumferential surface of the cylindricalroller 123 is formed as a concave curved surface corresponding to theconvex curved surface. However, the rolling contact surface 110 b may bea flat surface, and the cylindrical roller 123 may be a cylindricalsurface. In this regard, unlike the structure shown in FIG. 4, thecylindrical roller 123 itself hardly have a function of restraining arotational displacement of the rack shaft 110. Such a function isguaranteed by an urging member 130 described below.

FIG. 2A is a sectional view illustrating part of a rack-and-pinionsteering apparatus according to the present embodiment, cut off at adifferent position from the position in FIG. 1. FIG. 2B is a viewillustrating the configuration in FIG. 1 as viewed in the arrowdirection IIB. FIG. 2C is a view illustrating the configuration in FIG.2B, cut off by the line IIC-IIC as viewed in the arrow direction. FIG. 3is an extracted perspective view of a rack shaft, a cylindrical roller,and an urging member of the present embodiment. As shown in FIG. 3, therack shaft 110 is provided with rack teeth 110 a formed as far as thehalf of the entire length, and the remainder forms a cylindrical surface110 d.

In FIGS. 2A to 2C, an urging member 130 is disposed in a hole 101 dextending along the direction of the rack shaft 110 of the housing 101.Since the urging member 130 is annular, the urging member 130 can beeasily attached to, or detached from the housing 101 without using aconnecting member such as adhesive or a screw. However, the urgingmember 130 can be attached using adhesive supplementally as a matter ofcourse. For the urging member 130, polyacetal resin having an excellentcharacteristic in heat resistance and strength is preferable, but theurging member 130 is not limited to this.

As shown in FIG. 3, the urging member 130 is disposed at the portion onwhich the rack teeth 110 a are formed on the rack shaft 110, and formsan annular configuration surrounding the rack shaft 110. Also, theurging member 130 has a pair of the contact portions 130 b, 130 bcontacting the slanted surfaces 110 c, 110 c of the rack shaft 110.

As shown in FIG. 2B, each contact portion 130 b has an E-shapedstructure including a pair of extending parts 130 c, 130 c extendingform the annular parts of the urging member 130 along the slantedsurface 110 c of the rack shaft 110, a connecting part 130 d connectingeach end of the extending parts 130 c, 130 c, and a pressing part 130 ewhose one end is connected to the extending part 130 c and the other endextends in a cantilever state.

For the assembly of the urging member 130, in FIG. 2A, machine work isperformed on opposing surfaces (here, concave curved surfaces) 101 h,101 h of the housing 101 corresponding to the slanted surfaces 110 c,110 c of the rack shaft 110 to set the gaps between the pressing parts130 e, 130 e and the slanted surfaces 110 c, 110 c within an appropriaterange. Then the urging member 130 is attached to the hole 110 d suchthat the movement of the urging member 130 in the axial direction isconstrained using the work step between the work surface and the castingsurface.

As shown in FIG. 2C, both ends of each pressing part 130 e are broughtinto contact only with the slanted surfaces 110 c of the rack shaft 110,the central part of each pressing part 130 e is brought into contactonly with the hole 101 d of the housing 101. Since each pressing part130 e suppresses a rotational displacement and vibration of the rackshaft 110 about the axis line X with respect to the housing 101 by theelastic force thereof, it is possible to effectively suppress, forexample, the occurrence of rattling noise. Assuming that the thicknessof the pressing part 130 e is 3 to 5 mm, the gap Δ between the centralpart of the pressing part 130 e and the slanted surface 110 c should beabout 0.05 to 0.5 mm. The gap Δ should desirably be larger than themaximum amount of deformation of the disc sprint 124 of the supportingunit 120. This is because when an excessive force is applied between thepinion 103 a and the rack shaft 110 by a travelling wheel colliding witha paved step of sidewalk, for example, that force should be exerted onthe supporting unit 120, and should not be exerted on the pressing part130 e in order to prevent the contacting member 130 from being damaged.In this regard, if the corners contacting the rack shaft 110 at the endof each pressing part 130 e is rounded off, it becomes possible torestrain the lubricant adhered to the surface from being scraped whenthe rack shaft 110 relatively moves, and thus the lubricity can beimproved.

A description will be given of the operation of the present embodiment.When a steering force is inputted into an unillustrated steering wheel,the steering force is transmitted to the output shaft 103 through anunillustrated steering shaft. As shown in FIG. 3, the rotational forceof the output shaft 103 is converted into the longitudinal thrust of therack shaft 110 through the pinion 103 a and the rack teeth 110 a havingmeshing engagement with each other. The rack shaft 110 moves in thevertical direction of the page surface in the figure by the longitudinalthrust, thereby steering unillustrated wheels. At this time, thecylindrical roller 123 rolls on the rolling contact surface 110 b,allowing the rack shaft 110 to move with low friction.

As described in the present embodiment, the pressing force exerted onthe rack shaft 110 from the pinion 103 a is received by the cylindricalroller 123, and a rotational displacement of the rack shaft 110 issuppressed by the urging member 130, which is separated from thecylindrical roller 123. It is therefore possible to restrict the axialdirection size of the cylindrical roller 123, and thus the structure inthe vicinity of the pinion 103 a of the rack shaft 110 can be madecompact.

As described above, the present invention has been described in detailwith reference to the embodiment. The present invention, however, shouldnot be construed as being limited to the embodiment described above. Thepresent invention can be properly modified and improved as a matter ofcourse without departing from the spirit and scope of the invention.

1. A steering apparatus comprising: a housing; a rack shaft connected toa traveling wheel steering mechanism, having rack teeth formed at leaston part of an outer surface, and movably supported with respect to thehousing; and a pinion connected to a steering wheel and having meshingengagement with the rack teeth, wherein the rack shaft is provided witha rolling contact surface on the opposite side of the rack teeth acrossan axis line and a pair of surfaces extending in parallel with the axisline on both sides across the rolling contact surface, the apparatusfurther comprises a rolling member rolling on the rolling contactsurface of the rack shaft and an urging member having contact with thepair of surfaces and applying an urging force, wherein the urging memberis attached to the housing, forms an annular configuration surroundingthe entire circumference of the rack shaft, and has a contact portionhaving contact with the pair of surfaces to apply the urging force. 2.The steering apparatus according to claim 1, wherein the contact portionof the urging member comprises a pressing portion having the shape of acantilever.